In the process of polyethylene production, a small amount of oligomers, i.e. low relative molecular mass polyethylene, also known as polymer wax or polyethylene wax for short, is produced. It is widely used because of its excellent cold resistance, heat resistance, chemical resistance and wear resistance. In normal production, this part of wax as an additive can be added directly to the polyolefin processing, it can increase the light translation and processing performance of the product. Polymer wax is a good dulling agent for explosives, and it can also be used as a dispersing lubricant for plastics and pigments, moisture-proofing agent for corrugated paper, hot-melt adhesive and floor wax, and auto detailing wax.
Polymer wax is a non-toxic, tasteless, non-corrosive, white or slightly yellowish solid with relative molecular mass of 1800-8000. it has good chemical stability, excellent temperature resistance, chemical resistance and electrical properties at room temperature, and has a wide range of applications, and can be used as raw material for chlorinated polyethylene, modifier for plastics, coating agent for textiles and additive for improving the viscosity of crude oil and fuel oil. [1-2]
Foreign applications of low relative molecular mass polyethylene are widespread and in high demand. Japan produces about 3,000 tons per year, and the price is about twice as high as that of ordinary resins. Domestic demand is also increasing year by year although the start of the process is late, and the main manufacturers are Shanghai Jinshan, Nanjing Yangzi and Beijing University of Chemical Technology.
Application and mechanism of polymer wax in coatings
Waxes for coatings are mainly added in the form of additives, wax additives generally exist in the form of water emulsions and are initially used to improve the surface anti-expansion properties of the coating film. They are mainly used to improve the smoothness and scratch resistance of the coating film as well as to improve the water resistance. In addition, it can affect the rheological properties of the coating, and its addition can lead to a uniform orientation of solid particles such as aluminum powder in metallic glitter paints. It can be used as a matting agent in non-glossy paints, and the matting effectiveness of wax additives varies according to their particle size and particle size distribution. Therefore, wax additives are suitable for both glossy and non-glossy lacquers. Microcrystalline modified polyethylene waxes can be used to improve the surface properties of waterborne industrial coatings. Ffka-906, for example, has enhanced smoothness, anti-adhesion, anti-scratch and matting properties, and can effectively inhibit pigment precipitation. The addition amount is 0.25%-2.0%. 
1 Application methods
The use of waxes There are four common methods.
1. melting method: melting with solvent heated under a closed, high-pressure container, and then cooling under appropriate
The disadvantage is that the quality is not easily controlled, the operation is costly and dangerous, while some waxes are not suitable for this method.
2, Emulsification method: fine and round particles can be obtained, suitable for aqueous systems, but the added surfactant will affect the water resistance of the coating film.
3, Dispersion method: Add the wax to the tree wax/solution and disperse it by using ball mill, drum or other dispersion equipment; the disadvantage is that it is difficult to obtain high quality products and the cost is high.
4, Micro-powdering method: Micro-powdering method can use Jet-irniser or irniser/lassifier production process, that is, the use of coarse wax in a high-speed state between the fierce collision gradually broken into particles, and then by centrifugal centrifugal force, under the loss of weight is blown out and collected. This is the most used manufacturing method at present.
Although there are many methods of using wax, micronized wax is still the most used, and there are many different types of micronized waxes on the market, and the production processes of each manufacturer are different, so the particle size distribution, relative molecular mass, density, melting point, hardness and other properties of micronized waxes vary from factory to factory.
The manufacturing of polyethylene wax generally has high-pressure and low-pressure polymerization method; among them, the polyethylene wax with branched chain made by high-pressure method has lower density and melting temperature, while the low-pressure method can make straight-chain wax with low specific gravity; PE wax has various densities, for example, for the non-polar PE wax made by the same low-pressure method, usually the low density (low branched chain, high crystallinity) is harder and has better wear resistance and anti-traumatic properties, but It is less slippery and has a lower coefficient of friction. 
2 Characteristics and mechanism of waxes in coatings
There are many different types of waxes, and the form they show in the coating film we can roughly divide into the following three.
1, frosting effect: for example, when the melting point of the chosen wax is lower than the baking temperature, as the wax melts during baking
After the film is cooled, a thin layer of frost is formed on the coating surface.
2, Spherical axis effect: This effect lies in the wax from its own particle size and coating film thickness is similar, or even larger, and revealed, so that the wax scratch resistance, anti-scratch performance can be revealed.
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